1. Field of the Invention:
The present invention relates to thermionic cathodes and, more particularly, to improved materials and methods for preparing low-temperature, thermionic emitters.
2. Description of the Prior Art:
Contrary to the impression created by the manufacturers of solid state devices, the composition between solid state electron devices and vacuum devices has not been resolved. This is due in part to the fact that many operations such as those involving high frequency and high power can be performed only, or at least better in a vacuum device. The limitations of solid state devices and circuits in high temperature and high radiation ambients are well known.
Since many vacuum devices utilize thermionic emission, there is a continuous quest for improved emitters. The improvements usually sought are better efficiency and longer life without impairing the operation of the device. An emitter operating at temperatures lower than normal (.about.1,000.degree. K or .about.750.degree. C) is more efficient in terms of power consumption and has increased life expectancy because the cathode material is being evaporated at a slower rate.
The present invention is concerned with a provision of an alkaline earth oxide coated emitters that operate at temperature in the vicinity of 600.degree. C. Although evaporated BaO cathodes have been considered to have favorable characteristics, they do not perform as well as the commercially sprayed triple carbonate cathodes. Some sputtered triple carbonate cathodes have higher emission densities than sprayed cathodes, but reproducibility is poor and performance deteriorates with time. Moreover, these cathodes do not exhibit favorable current densities and life expectancies at reduced temperatures and it is difficult to apply a delineated pattern to the cathode substrate by the techniques utilized to apply and activate the alkaline earth oxide coatings.